Antenna assemblies for medical applications

ABSTRACT

A device for directing energy to a target volume of tissue includes a monopole antenna assembly that includes a monopole antenna radiating section having a monopole antenna element surrounded by a dielectric material. The monopole antenna assembly also includes a ground plane disposed at a proximal end of the monopole antenna radiating section, wherein the ground plane is configured to direct energy into the target volume of tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/250,171, filed Oct. 13, 2008, the entirecontents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to antennas and, more particularly, toelectrosurgical devices with antenna assemblies suitable for use intissue ablation applications.

2. Discussion of Related Art

Treatment of certain diseases requires destruction of malignant tumors.Electromagnetic radiation can be used to heat and destroy tumor cells.Treatment may involve inserting ablation probes into tissues wherecancerous tumors have been identified. Once the probes are positioned,electromagnetic energy is passed through the probes into surroundingtissue.

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures that areslightly lower than temperatures normally injurious to healthy cells.Known treatment methods, such as hyperthermia therapy, useelectromagnetic radiation to heat diseased cells to temperatures above41° C. while maintaining adjacent healthy cells below the temperature atwhich irreversible cell destruction occurs. These methods involveapplying electromagnetic radiation to heat, ablate and/or coagulatetissue. Microwave energy is sometimes utilized to perform these methods.Other procedures utilizing electromagnetic radiation to heat tissue alsoinclude coagulation, cutting and/or ablation of tissue.

Electrosurgical devices utilizing electromagnetic radiation have beendeveloped for a variety of uses and applications. A number of devicesare available that can be used to provide high bursts of energy forshort periods of time to achieve cutting and coagulative effects onvarious tissues. There are a number of different types of apparatus thatcan be used to perform ablation procedures. Typically, microwaveapparatus for use in ablation procedures include a microwave generator,which functions as an energy source, and a microwave surgical instrumenthaving an antenna assembly for directing the energy to the targettissue. The microwave generator and surgical instrument are typicallyoperatively coupled by a cable assembly having a plurality of conductorsfor transmitting microwave energy from the generator to the instrument,and for communicating control, feedback and identification signalsbetween the instrument and the generator.

Microwave energy is typically applied via antenna assemblies that canpenetrate tissue. Several types of antenna assemblies are known, such asmonopole, dipole and helical. In monopole and dipole antenna assemblies,microwave energy generally radiates perpendicularly away from the axisof the conductor. Helical antenna assemblies have two main modes ofoperation: normal mode (broadside) and axial mode (endfire). In thenormal mode of operation, the field radiated by the helix is maximum ina perpendicular plane to the helix axis. In the axial mode, maximumradiation is along the helix axis.

A typical helical antenna is illustrated in FIG. 1 and includes aconducting wire 100 that is coiled to form a helix having an axis 120and backed by a conducting ground plane 110. The basic geometricalparameters that define a helical antenna include the diameter D andcircumference C of the helix, where C=πD, the number of turns N of thehelix, the center-to-center spacing S between turns, the pitch angle α,where α=arc tan (S/πD), and the axial length A of the helix, whereA=N×S. When the circumference of the helix is small compared with theaxial length and the wavelength, the helical antenna radiates in thenormal mode (similar to dipole antenna radiation). When the helixcircumference is about one wavelength, the helical antenna operates inthe axial mode. Typically, a helical antenna radiates in the normal modewhen C<0.4λ (λ is the wavelength) and in the axial mode forapproximately 0.75λ<C<1.3λ.

During certain procedures, it can be difficult to assess the extent towhich microwave energy will radiate into the surrounding tissue, makingit difficult to determine the area or volume of the target tissue thatwill be ablated.

SUMMARY

The present disclosure relates to a device for directing energy to atarget volume of tissue including a monopole antenna assembly thatincludes a monopole antenna radiating section having a monopole antennaelement surrounded by a dielectric material. The monopole antennaassembly also includes a ground plane disposed at a proximal end of themonopole antenna radiating section, wherein the ground plane isconfigured to direct energy into the target volume of tissue.

The present disclosure also relates to a device for directing energy toa target volume of tissue including a ground plane and a number ofmonopole antenna assemblies N, where N is an integer greater than 1.Each monopole antenna assembly includes a monopole antenna radiatingsection having a monopole antenna element surrounded by a dielectricmaterial, wherein a proximal end of each monopole antenna radiatingsection is electrically coupled to the ground plane. The device alsoincludes a power splitter to drive energy into each of the N monopoleantenna assemblies, wherein the power splitter is electrically coupledto each monopole antenna element.

Objects and features of the presently disclosed antenna assemblies willbecome readily apparent to those of ordinary skill in the art whendescriptions of embodiments thereof are read with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the basic geometry of a helicalantenna;

FIG. 2 is a schematic diagram of a helical antenna assembly, accordingto an embodiment of the present disclosure;

FIG. 3 is a perspective view of the helical antenna assembly illustratedin FIG. 2 showing the transmission pattern in axial mode;

FIG. 4 is a schematic diagram of a helical antenna assembly, accordingto an embodiment of the present disclosure;

FIG. 5 is a schematic diagram of an electrosurgical device includingthree helical antenna assemblies, according to an embodiment of thepresent disclosure;

FIG. 6A is a schematic diagram of another embodiment of a helicalantenna assembly, according to the present disclosure;

FIG. 6B is a perspective view of a portion of the helical antennaassembly shown in FIG. 6A taken along the lines II-II;

FIG. 7 is a cross-sectional view of the helical antenna assembly of FIG.6B;

FIG. 8 is a cross-sectional view of the helical antenna assembly of FIG.6B shown with a dielectric material located in an interior of thehelical antenna element, according to an embodiment of the presentdisclosure;

FIG. 9A is a schematic diagram of another embodiment of a helicalantenna assembly, according to the present disclosure;

FIG. 9B is a perspective view of a portion of the helical antennaassembly shown in FIG. 9A;

FIG. 10 is a perspective view of the helical antenna assembly of FIG. 9Bshown with a circulating fluid, according to an embodiment of thepresent disclosure;

FIG. 11A is a schematic diagram of yet another embodiment of a helicalantenna assembly, according to the present disclosure;

FIG. 11B is a perspective view of a portion of the helical antennaassembly shown in FIG. 11A;

FIG. 12 is a flowchart illustrating a method for directing energy to atarget volume of tissue, according to an embodiment of the presentdisclosure;

FIGS. 13A and 13B are schematic diagrams of a helical antenna assemblyincluding a moveable shell, according to an embodiment of the presentdisclosure;

FIG. 14 is a perspective view of a helical antenna assembly, accordingto an embodiment of the present disclosure, positioned at the surface ofthe target tissue, prior to the operation of the helical antennaassembly;

FIG. 15 is a schematic diagram of a monopole antenna assembly, accordingto an embodiment of the present disclosure;

FIG. 16 is a perspective view of the monopole antenna assembly of FIG.15 showing the transmission pattern;

FIG. 17 is a schematic diagram of the monopole antenna assembly of FIGS.15 and 16, positioned in the target surgical site, schematicallyillustrating thermal effects of microwave energy radiated into a portionof biological tissue;

FIGS. 18A and 18B are schematic diagrams of electrosurgical devicesincluding multiple monopole antenna assemblies, according to embodimentsof the present disclosure; and

FIG. 19 is a schematic diagram of an electrosurgical device includingmultiple monopole antenna assemblies, according to an embodiment of thepresent disclosure, positioned in the target surgical site,schematically illustrating thermal effects of microwave energy radiatedinto a portion of biological tissue.

DETAILED DESCRIPTION

Hereinafter, embodiments of the presently disclosed antenna assemblieswill be described with reference to the accompanying drawings. Likereference numerals may refer to similar or identical elements throughoutthe description of the figures.

As used herein, the phrase “ablation procedure” generally refers to anyablation procedure, such as microwave ablation or microwave ablationassisted resection. As used herein, the term “microwave” generallyrefers to electromagnetic waves in the frequency range of 300 megahertz(MHz) (3×10⁸ cycles/second) to 300 gigahertz (GHz) (3×10¹¹cycles/second). As used herein, the phrase “transmission line” generallyrefers to any transmission medium that can be used for the propagationof signals from one point to another.

Various embodiments of the present disclosure provide electrosurgicaldevices for treating tissue and methods of directing electromagneticradiation to a target volume of tissue. Embodiments may be implementedusing electromagnetic radiation at microwave frequencies or at otherfrequencies. A helical antenna assembly, according to variousembodiments, is capable of radiating in axial and normal modes atdifferent stages during the course of a procedure, such as an ablationprocedure. Tissue can be ablated around the antenna's radiating sectionand distal to the radiating section without repositioning the helicalantenna assembly. Multiple helical antenna assemblies can be employed invariously arranged configurations. For example, multiple helical antennaassemblies can be placed parallel to each other to substantiallysimultaneously ablate a target volume of tissue.

Various embodiments of the presently disclosed helical antenna assemblyare suitable for microwave ablation and/or for use to pre-coagulatetissue for microwave ablation assisted surgical resection. Althoughvarious methods described hereinbelow are targeted toward microwaveablation and the complete destruction of target tissue, it is to beunderstood that methods for directing electromagnetic radiation may beused with other therapies in which the target tissue is partiallydestroyed or damaged, such as, for example, to prevent the conduction ofelectrical impulses within heart tissue.

An electrosurgical device including a helical antenna assembly,according to various embodiments, can be used initially in an axial modeto perform ablation distally, and subsequently in a normal mode toperform ablation in areas surrounding the antenna's radiating section.Alternatively, the electrosurgical device can be used initially in anormal mode to perform ablation in areas surrounding the antenna'sradiating section, and secondly in an axial mode to ablate in distalareas. It is to be understood that the duration of axial and normalmodes of operation and the sequencing of axial and normal modes ofoperation may be varied depending on the particular application of thehelical antenna assembly.

FIGS. 2 and 3 show a helical antenna assembly according to an embodimentof the present disclosure. Referring to FIG. 2, the helical antennaassembly 200 includes a helical antenna element 210, a ground plane 220,a connector 250 that is coupled to the helical antenna element 210, anda housing 230. Helical antenna element 210 can be formed of any suitablematerial, such as steel, beryllium copper or silver-plated copper. Theouter diameter D of the helical antenna element 210 and the number ofturns of the helical antenna element 210 may be varied depending on theparticular application of the helical antenna assembly. Housing 230 isformed of a dielectric or electrically non-conductive material, such asa non-conductive polymer. Housing 230 may be configured in a variety ofshapes and sizes depending on a particular surgical purpose or toaccommodate a particular surgical need. Referring to FIG. 3, the helicalantenna assembly 200 is shown operating in an axial mode, whereby thetransmission pattern 310 radiates outwardly from the distal end of thehelical antenna assembly 200.

FIG. 4 shows a helical antenna assembly according to another embodimentof the present disclosure. Referring to FIG. 4, the helical antennaassembly 400 is shown positioned for the delivery of electromagneticenergy, such as microwave energy, to the targeted volume 480 of thetissue “T”. When the helical antenna assembly 400 radiates in an axialmode, as indicated by the downward arrow, a portion 443 of the tissue“T” is abated distal to the helical antenna radiating section. When thehelical antenna assembly 400 radiates in the normal mode, as indicatedby the left and right arrows, a portion 445 of the tissue “T” is abatedaround the helical antenna radiating section. The helical antennaradiating section will be described later in this disclosure withreference to FIGS. 6A and 6B. A dielectric material, e.g., a dielectricgel, may be used between the helical antenna radiating section and thetissue “T” to improve coupling.

FIG. 5 shows an electrosurgical device including three helical antennaassemblies according to another embodiment of the present disclosure.The electrosurgical device 500 includes a first helical antenna assembly510A, a second helical antenna assembly 510B, a third helical antennaassembly 510C, and a housing portion 580 coupled to a transmission line550. Housing portion 580 may be formed of any suitable material, such asmetal or plastic or combination thereof. The shape and size of thehousing portion 580 may be varied from the configuration depicted inFIG. 5.

Although first, second and third helical antenna assemblies 510A, 510Band 510C, respectively, extend longitudinally from the distal end of thehousing portion 580 and are arranged substantially equally spaced apartand substantially parallel to each other, the number, shape, size andrelative spacing of the helical antenna assemblies may be varied fromthe configuration depicted in FIG. 5. For example, an electrosurgicaldevice may include six helical antenna assemblies, arranged in atwo-by-three matrix, or other suitable pattern, to substantiallysimultaneously ablate a larger target volume of tissue. It iscontemplated herein that an electrosurgical device may utilize anynumber of helical antenna assemblies (or any number of sets of one ormore helical antenna assemblies), each helical antenna assembly (or setof helical antenna assemblies) being operable independently orsubstantially simultaneously with respect to any number of other helicalantenna assemblies (or sets of helical antenna assemblies).

First, second and third helical antenna assemblies 510A, 510B and 510Cmay be axially rigid to allow for tissue penetration. For example,first, second and third helical antenna assemblies 510A, 510B and 510Cmay be sufficiently small in diameter to be minimally invasive of thebody, which may reduce the preparation time of the patient as might berequired for more invasive penetration of the body. As shown in FIG. 6A,a helical antenna assembly 600 includes a tip 665, which isadvantageously configured to facilitate penetration of tissue. Thefirst, second and third helical antenna assemblies 510A, 510B and 510Cmay also include tip portions. The helical antenna assemblies 510A, 510Band 510C are inserted directly into tissue, through a lumen, such as,for example, a vein, needle or catheter, placed into the body duringsurgery by a clinician, or positioned in the body by other suitablemethods. The electrosurgical device 500 may include any combination ofhelical antenna assemblies (e.g., 510A, 510B and 510C) and/or monopoleantenna assemblies (e.g., 1920 shown in FIG. 19).

Electrosurgical device 500 may include a power splitter (not shown),disposed within the housing portion 580, to drive energy into each ofthe first, second and third helical antenna assemblies 510A, 510B and510C. Transmission line 550 is coupled to an electrosurgical generator(not shown) for generating an output signal. A first frequency f₁ isused for axial mode (first wavelength λ₁) and a second frequency f₂ isused for normal mode (second wavelength λ₂,). For example, λ₂ may beapproximately two to three times larger than λ₁ and the circumference Cof the helix may be in the range of about 0.8λ₁ to about 1.2λ₁ and suchthat C<0.4λ₂.

Referring to the embodiment shown in FIG. 6A, the helical antennaassembly 600 includes a helical antenna radiating section 660 and a tipportion 665. Tip portion 665 is advantageously configured forpenetrating tissue. Although the surfaces of the tip portion 665 shownin FIG. 6A are generally flat, that surfaces of the tip portion 665according to various embodiments may be curved or may include acombination of flat, sloped or curved portions. The shape and size ofthe tip portion 665 may be varied from the configuration depicted inFIG. 6A. The helical antenna radiating section 660 includes a helicalantenna element 610, a sleeve member 621 located at the periphery of thehelical antenna element 610 coaxially with the helical antenna element610, and a shell 630 located at the periphery of the sleeve member 621.Helical antenna element 610 may be formed of a shape-memory material,such as copper-zinc-aluminum-nickel, copper-aluminum-nickel and/ornickel-titanium (NiTi) alloys, e.g., to adjust shape of the helicalantenna assembly 600 with different temperature perfused fluid.

FIG. 6B shows the helical antenna radiating section 660, whichcorresponds to the portion of the helical antenna assembly 600 in FIG.6A taken along the lines II-II. In one embodiment, the sleeve member 621is formed of a dielectric material and may include a material that hasvariable dielectric constant, or adjustable dielectric constant, so thateffective wavelengths will vary between the axial mode and the normalmode of operation. In one embodiment, the helical antenna radiatingsection 660 includes a second dielectric material 880 (see FIG. 8)disposed to the interior of the helical antenna element, wherein thesleeve member 621 and the second dielectric material 880 havesubstantially similar dielectric properties. Sleeve member 621 may beformed of an inflatable element, a shape-memory alloy element,magneto-electrical actuated elements, or other activateable elements toexpand the helical antenna radiating section to varied dimensions. Shell630 encircles the sleeve member 621 and may be formed of a conductivematerial to improve directionality and to reduce stray electromagneticradiation emissions. In one embodiment, the shell (1320 shown in FIGS.13A and 13B) is adapted to be slideably moveable along the periphery ofthe sleeve member (1360 shown in FIGS. 13A and 13B).

Referring to FIG. 6B, the helical antenna radiating section 660 includesa distal end 664. Helical antenna assembly 600 can be operated in theaxial mode to perform a procedure on a first portion of a target volumeof tissue, wherein the first portion of the tissue is located distal toend 664 of the helical antenna assembly 600. Helical antenna assembly600 can be operated in the normal mode to perform a second procedure ona second portion of the target volume of tissue, wherein the secondportion is located substantially adjacent to the helical antennaradiating section 660. It is to be understood that various sequences ofaxial and normal modes of operation may be utilized depending on theparticular application of the helical antenna assembly 600.

FIG. 7 is a cross-sectional view of the helical antenna assembly of FIG.6B. FIG. 7 shows the helical antenna assembly 600 including the helicalantenna element 610 enclosed by a first dielectric material 721, and theshell 630 which surrounds the length of the first dielectric material721. First dielectric material 721 may include ferroelectric dielectricmaterials, which through applied DC voltage may allow control of thedepth and spread of the power deposition pattern. Shell 630 may beformed of an electrically conductive material, e.g., metal, and may beused as the charge accumulation conductor generating the DC field, withthe helix being the opposite electrode. Located to the interior of thehelical antenna element 610 is a cavity 680. As described hereinbelow,interior cavity 680 may include a dielectric material disposed therein.

FIG. 8 is a cross-sectional view of the helical antenna assembly of FIG.6B shown with a dielectric material disposed to the interior of thehelical antenna element, according to an embodiment of the presentdisclosure. The antenna assembly 800 of FIG. 8 is similar to the helicalantenna assembly 600 shown in FIG. 7, except that the helical antennaassembly 800 includes a second dielectric material 880 disposed to theinterior of the helical antenna element 610, i.e., instead of theinterior cavity 680. In one embodiment of helical antenna assembly 800,the first dielectric material 721 and the second dielectric material 880have substantially similar dielectric properties. In other embodiments,the dielectric properties may be substantially higher or lower inε_(r)′, ε_(r).″ Second dielectric material 880 may include ferroelectricdielectric materials. Enclosing the helical antenna element 610 and thedielectric load, e.g., first and second dielectric materials 721 and880, with conductive shell 630 may aid directionality of the helicalantenna assembly 800. Shell 630 may be longitudinally divided into aplurality of electrodes with a dielectric material disposed between theelectrodes, for beam steering, e.g., through ferroelectric manipulation.

FIGS. 9A and 9B show a helical antenna assembly according to anotherembodiment of the present disclosure, wherein the helical antennaassembly 900 includes a helical antenna element 910, a fluid 922, anouter shell 930, and a tip 965. Tip 965 is advantageously configured tofacilitate penetration of tissue. Helical antenna assembly 900 alsoincludes an inner shell, located at the periphery of the helical antennaelement 910 and surrounding the length of the helical antenna element910, and two longitudinally formed partitions, which form a firstchannel 915 and a second channel 925 in the space between the outershell 930 and the periphery of the helical antenna element 910. Each ofthe first and second channels 915, 925 are utilized to hold the fluid922. In one embodiment, each of the longitudinally formed partitionsinclude a number of openings formed therein for placing the first andsecond channels 915, 925 in fluid communication. In the embodimentillustrated in FIG. 9B, the first and second channels 915 and 925 havesubstantially equal dimensions. Although two channels are shown in FIG.9B, the helical antenna assembly 900 may include a single channel ormultiple channels.

FIG. 10 shows a helical antenna assembly according to yet anotherembodiment of the present disclosure, wherein the helical antennaassembly 1000 includes a helical antenna element 1010 and an outer shell1030. The helical antenna assembly 1000 also includes a first channel1015 and a second channel 1025, which are similar to the first andsecond channels 915, 925 shown in FIG. 9B, except that the distal endportions of the first and second channels 1015, 1025 are adapted toallow fluid circulation in opposing directions, as indicated by theright and left arrows. Fluids having different dielectric constants εare circulated around the helical antenna radiating section, and theeffective wavelength changes depending on the fluid dielectricproperties. The relationship between the circumference C of the helicalantenna element 1010 and the effective wavelength λ can be expressed bythe equation I=C/(f×sqrt(ε)), where frequency f=1/λ. For example, incases when the dielectric constant ε₁ of a first fluid is in the rangeof about three to nine times the dielectric constant ε₂ of a secondfluid, 0.8λ₁<C<1.2λ₁ and C<0.4λ₂. In one embodiment wherein fluids arecirculated around the helical antenna radiating section, and whereinhelical antenna element 1010 is formed of a shape memory alloy, thefluid temperature is varied to change the shape of the helical antennaassembly 1100, for example, to assist with altering normal versusendfire mode.

FIGS. 11A and 11B show a helical antenna assembly 1100 that includes ahousing 1165, a helical antenna element disposed with the housing 1165and backed by a conducting ground plane 1120, and a connector 1150 whichis coupled to the helical antenna element. Helical antenna assembly 1100is shown operating in an axial mode, whereby the transmission pattern1143 extends outwardly from the distal end of the helical antennaassembly 1100. Referring to FIG. 11B, the helical antenna assembly 1100also includes a dielectric element 1180 and a cavity 1170 definedbetween the outer shell of the housing 1165 and the periphery of thedielectric element 1180. Cavity 1170 includes channels for holding afluid, e.g., first and second channels 915 and 925 for holding fluid 922as shown in FIG. 9B.

FIG. 12 is a flowchart illustrating a method for directing energy to atarget volume of tissue, according to an embodiment of the presentdisclosure. In step 1210, a helical antenna assembly, e.g., 400, ispositioned for the delivery of energy to the target volume of tissue.The helical antenna assembly 400 may be inserted directly into tissue(e.g., as shown in FIG. 4), inserted through a lumen, e.g., a vein,needle or catheter, placed into the body during surgery by a clinician,or positioned in the body by other suitable methods.

In step 1220, the helical antenna assembly is operated in a first mode(e.g., a normal mode) of operation to perform a first procedure on afirst portion of the target volume of tissue, the first portion beinglocated substantially adjacent to a longitudinal portion of the helicalantenna assembly.

In step 1230, the helical antenna assembly is operated in a second mode(e.g., an axial mode) of operation to perform a second procedure on asecond portion of the target volume of tissue, the second portion beinglocated distal to an end portion of the helical antenna assembly.

FIGS. 13A and 13B show a helical antenna assembly 1300 including amoveable shell 1320 located at a periphery of a sleeve member 1360coaxially disposed with respect to sleeve member 1360. Shell 1320 isadapted to be slideably moveable along the periphery of the sleevemember 1360 between a first position, in which an outer diametrical wallof the sleeve member 1360 is entirely covered by the shell 1320 (seeFIG. 13A), and a second position, in which at least a portion of theouter diametrical wall of the sleeve member 1360 is exposed (see FIG.13B). In one embodiment, when the helical antenna assembly 1300 isoperated in the normal mode, the shell 1320 is positioned in the secondposition. In another embodiment, when the helical antenna assembly 1300is operated in the axial mode, the shell 1320 may be positioned ineither the first or second position. Shell 1320 shown in FIGS. 13A and13B is a substantially cylindrically-shaped structure having an innerdiameter “D_(I)”, which is larger than an outer diameter “D_(O)” of thesleeve member 1360. Shell 1320 may be slideably movable to variouspositions such that any portion of the helical radiating section of thehelical antenna assembly 1300 may be exposed for radiating the tissue“T”.

FIG. 14 illustrates a helical antenna assembly 1400 that includes ahelical antenna element 1440 disposed with a housing 1430 and backed bya conducting ground plane 1450 and a connector 1420, which iselectrically coupled to the helical antenna element 1440 and atransmission line 1410. Helical antenna element 1440 may be configuredas a dielectrically-loaded endfire helical antenna, which may besuitable for microwave ablation and/or for use to pre-coagulate tissuefor microwave ablation assisted surgical resection. Helical antennaassembly 1400 may have an endfire radiation pattern similar to theendfire radiation pattern 310 of helical antenna assembly 200 shown inFIG. 3.

In one embodiment of helical antenna assembly 1400, a substantiallycylindrically-shaped dielectric material is disposed within the housing1430. The dielectric material within the housing 1430 may have a highpermittivity such that the wavelength of the electromagnetic radiation,e.g., microwave radiation, transmitted by the helical antenna assembly1400 is short enough to allow for a compact design. Helical antennaassembly 1400 may be configured in a variety of shapes and sizesdepending on a particular surgical purpose or to accommodate aparticular surgical need.

In one embodiment of helical antenna assembly 1400, the helical antennaelement 1440 is formed of a shape-memory alloy, and the temperature of afluid circulated around the helical antenna radiating section is variedto expand the circumference of the helical antenna radiating sectionand/or reduce the circumference of the helical antenna radiatingsection.

During various non-invasive procedures, the distal end of the helicalantenna assembly 1400 may be placed in contact with the surface of atarget tissue “T”. In this instance, the endfire power would allow fortargeting of surface tissue “T” placed in contact with the helicalantenna assembly 1400. Layers of various metals and/or dielectric aroundthe substantially cylindrically-shaped dielectric material disposedwithin the housing 1430 may be utilized to improve power delivery anddirectionality into surface tissue “T” and/or provide for a sterilizabledevice. A dielectric material, e.g., a dielectric gel, may be usedbetween the distal end of the helical antenna assembly 1400 and thetissue “T”, e.g., to improve coupling.

FIG. 15 is a schematic diagram of a monopole antenna assembly 1500 thatincludes a monopole radiating section 1550 including a monopole antennaelement 1510 surrounded by a dielectric material 1520 and backed by aground plane 1530, a tip 1505, and a connector 1545, which iselectrically coupled to the monopole antenna element 1510 and atransmission line 1540. Ground plane 1530 is configured to direct theelectromagnetic radiation, e.g., microwave radiation, into the targetedtissue and may provide a boundary to define the resonant frequency ofthe monopole antenna assembly 1500. In one embodiment, dielectricmaterial 1520 reduces the operating wavelength of the monopole radiatingsection 1550 and may buffer the microwave wavelength from tissueelectrical property dynamics. FIG. 16 shows the transmission pattern ofthe monopole antenna assembly 1500.

FIG. 17 shows the monopole antenna assembly 1500 of FIGS. 15 and 16,positioned in the target surgical site, following the operation of themonopole antenna assembly 1500. FIG. 17 schematically illustratesthermal effects of microwave energy radiated into tissue “T”, whereby aportion 1770 of the tissue “T” is abated around the monopole antennaassembly 1500.

FIGS. 18A and 18B illustrate electrosurgical devices including multiplemonopole antenna assemblies 1820. Components of the monopole antennaassemblies 1820 of FIGS. 18A and 18B may be similar to components of themonopole antenna assembly 1500 shown in FIGS. 15-17 (e.g., a monopoleradiating section 1550 including the monopole antenna element 1510,dielectric material 1520, and tip 1505), and further description thereofis omitted in the interests of brevity. Various numbers andconfigurations of monopole antenna assemblies 1820 may utilize the sameground plane. For example, an electrosurgical device 1801 shown in FIG.18A includes a substantially cylindrically-shaped housing 1810configured with ten monopole antenna assemblies 1820 that are arrangedsubstantially parallel to each other and which longitudinally extendfrom the distal end of the housing 1810. Referring to FIG. 18B, theelectrosurgical device 1802 includes a substantially rectangular-shapedhousing 1830 configured with sixteen monopole antenna assemblies 1820that are arranged substantially parallel to each other in alongitudinally extending manner from the distal end of the housing 1830and aligned in a pattern of rows and columns.

FIG. 19 shows an electrosurgical device 1900 that includes six monopoleantenna assemblies 1920 that are commonly backed by a ground plane 1950.Each monopole antenna assembly 1920 includes a monopole antenna element1930 surrounded by a dielectric material 1940. Ground plane 1950 isconfigured to direct the electromagnetic radiation, e.g., microwaveradiation, into the target surgical site and may provide a boundary todefine the resonant frequency of the respective monopole antennaassemblies 1920. The monopole antenna assemblies 1920 are inserteddirectly into tissue, through a lumen, such as, for example, a vein,needle or catheter, placed into the body during surgery by a clinician,or positioned in the body by other suitable methods.

Electrosurgical device 1900 also includes a power splitter 1950 thatdrives energy into each of the monopole antenna assemblies 1920, whichis electrically coupled to each of the respective monopole antennaelements 1930. In one embodiment, power splitter 1950 is a microwavepower splitter 1950.

Microwave power splitter 1950 may be implemented by any suitable powerdivider that provides substantially equal power split at all outputports. Microwave power splitter 1950 may be implemented by any suitablepower divider that provides equal power split at all output ports whilesubstantially maintaining phase and amplitude balance. For example, inone instance, the microwave power splitter 1950 implements using a 6-waypower divider that provides equal power split at all output ports whilemaintaining a phase balance of <+/−10 degrees and amplitude balance of<1.5 dB.

Electrosurgical device 1900 also includes a connector 1965, which iselectrically coupled to the power splitter 1950 and a transmission line1960. Transmission line 1960 includes proximal and distal ends and maybe suitable for transmission of microwave energy. The proximal end ofthe transmission line 1960 may be coupled to a microwave energy source(not shown), and the distal end thereof is in communication with theconnector 1965 of the monopole antenna assembly 1900.

Although embodiments have been described in detail with reference to theaccompanying drawings for the purpose of illustration and description,it is to be understood that the inventive processes and apparatus arenot to be construed as limited thereby. It will be apparent to those ofordinary skill in the art that various modifications to the foregoingembodiments may be made without departing from the scope of thedisclosure.

What is claimed is:
 1. A helical antenna assembly for directing energyto a target volume of tissue, comprising: a helical antenna element; anouter shell coaxially disposed about the helical antenna element; a tipportion located at a distal end of the helical antenna element; and aconducting ground plane configured to direct energy into the targetvolume of tissue, wherein the helical antenna element extends outwardlyfrom the conducting ground plane.
 2. The helical antenna assembly ofclaim 1, further comprising a sleeve member coaxially disposed about thehelical antenna element.
 3. The helical antenna assembly of claim 2,wherein the sleeve member is formed of a dielectric material.
 4. Thehelical antenna assembly of claim 2, wherein the sleeve member is formedof an inflatable element, a shape-memory alloy element, or amagneto-electrical actuated element.
 5. The helical antenna assembly ofclaim 2, wherein the outer shell is configured to slideably move aboutthe sleeve member in coaxial relation therewith.
 6. The helical antennaassembly of claim 1, wherein the helical antenna element is formed of ashape-memory material.
 7. The helical antenna assembly of claim 6,wherein the shape memory material is copper-zinc-aluminum-nickel,copper-aluminum-nickel, or nickel-titanium.
 8. The helical antennaassembly of claim 1, wherein the outer shell is formed of a conductivematerial.
 9. The helical antenna assembly of claim 1, further comprisinga dielectric material disposed in an interior area defined by thehelical antenna element.
 10. The helical antenna assembly of claim 1,further comprising an inner shell disposed within the outer shell andabout the helical antenna element, the inner shell extending an entirelength of the helical antenna element.
 11. The helical antenna assemblyof claim 10, further comprising two longitudinally formed partitionsthat form a first channel and a second channel in a space between theouter shell and the inner shell.
 12. The helical antenna assembly ofclaim 1, further comprising: a housing portion; and at least one furtherhelical antenna element, wherein the helical antenna element and the atleast one further helical antenna element are coupled to the housingportion and extend longitudinally from a distal end of the housingportion.